Granular surfactant compositions are principally prepared by spray or drum drying. In the spray drying process the surfactant components, plus perhaps salts and builders, are mixed with as much as 35-50% water to form a slurry. The slurry obtained is heated and spray dried, which is expensive.
Such spray drying requires 30-40 wt.% of the water to be removed. The spray drying equipment used is expensive. The granule obtained has good solubility but a low bulk density, so the packing volume is large. The particles also may be sticky, particularly when hot, and thus wall buildup is an additional problem. There are other known disadvantages in preparing granular materials by spray drying, such as environmental concerns and heat sensitivity. An agglomeration process, on the other hand, would be cleaner, as well as less expensive, both in terms of equipment and operating costs.
There are many prior art nonspray-drying processes which produce surfactant granules. Most, however, require mixing of the surfactant with other materials such as inorganic salts or aluminosilicate-type materials. Some other processes require use of an acid form of the surfactant to work. In most cases, a diluted surfactant particle is obtained. The major problem with the use of a high active surfactant paste as a starting material in a one step granulation process is its stickiness.
In U.S. Pat. No. 4,515,707, Brooks, issued May 7, 1985; Japanese laid-open Appln. No. 183540/1983, Kao Soap Co., Ltd., filed Sept. 30, 1983; and Japanese Sho. 61-118500, Lion K.K., June 5, 1986, high shear and/or cold mixing processes are disclosed. Typically, excess carbonate is required (2-10 molar excess) to assure reasonable conversion of the surfactant acids. Excess carbonate adversely drives up the wash water pH to the very alkaline range which can be undesirable, particularly for some nil-phosphate formulas and formulas containing peracid bleaches. Such high shear and cold mixing processes are known, but they have drawbacks, e.g., some require an extra grinding step or some other action, as well as the addition of other ingredients, primarily solids. Others use a dry neutralization technique for mixing the acid form of the surfactant with sodium carbonate.
A practical problem with the use of a surfactant acid form is that it requires immediate use after it is made, or cool temperature storage, for such highly reactive acids, such as the alkyl sulfate acids, are subject to degradation unless cooled. They also tend to undergo hydrolysis during storage, forming free sulfuric acid and alcohol. In practical terms, such prior art processes require close-coupling of surfactant acid production with granulation which requires an additional capital investment.
In U.S. Pat. No. 4,162,994, Kowalchuk, issued July 31, 1979, it is disclosed that calcium salts are required to overcome problems in processing by nonspray drying (i.e., mechanical) means formulations based on sodium salts of anionic surfactants and certain nonionic surfactants. A drawback to that process is that insoluble calcium salts can lower the solubility of the formulation, which is of particular importance in stress situations, such as in pouch-type executions.
U.S. Pat. No. 4,427,417, Porasik, issued Jan. 24, 1984, v discloses preparing granular detergent compositions from hydratable particulate detergent salts, etc., under conditions insuring complete hydration and agglomerating them into storage stable, dry, pourable agglomerates. This patent is incorporated herein by reference.